str_extract specific patterns (example)

r, regex

Solution

You can try

library(stringr)
str_extract(str2, "[A-Z][0-9]{4,5}[A-Z]?")
#[1] "A1234B"  "A12345B" "A12345"

Here, the pattern looks for a capital letter `[A-Z]`, followed by `4` or 5 digits `[0-9]{4,5}`, followed by a capital letter `[A-Z]` `?`

Or you can use `stringi` which would be faster

library(stringi)
 stri_extract(str2, regex="[A-Z][0-9]{4,5}[A-Z]?")
 #[1] "A1234B"  "A12345B" "A12345"

Or a `base R` option would be

 regmatches(str2,regexpr('[A-Z][0-9]{4,5}[A-Z]?', str2))
 #[1] "A1234B"  "A12345B" "A12345"

data

str2 <- c('_A00_A1234B_', '_A00_A12345B_', '_A1_A12345_')

Problem

I'm still a little confused by regex syntax. Can you please help me with these patterns: ``` _A00_A1234B_ _A00_A12345B_ _A1_A12345_ ``` my approaches so far: ``` vapply(strsplit(files, "[_.]"), function(files) files[nchar(files) == 7][1], character(1)) ``` or ``` str_extract(str2, "[A-Z][0-9]{5}[A-Z]") ``` The expected outputs are ``` A1234B A12345B A12345 ``` Thanks!

Original source